1. Field of the Invention
The present invention relates to a vacuum pump, such as a turbo-molecular pump, which produce a vacuum by using the rotation of its rotor, used for a semiconductor manufacturing apparatus, an electron microscope, a surface analyzing apparatus, a mass spectroscope, a particle accelerator, a nuclear fusion experiment apparatus
2. Description of the Related Art
For example, a process such as dry etching process or chemical vapor deposition (CVD) of semiconductor manufacturing process is required to be performed in a vacuum environment, and a vacuum pump such as a turbo-molecular pump having a high-speed rotor is used to produce such a vacuum.
As a conventional vacuum pump, for example, it is disclosed in Japanese Utility Model Application No. Hei.4-52644 (Kokai-publication No.Hei.6-14491). In this type of vacuum pump, as shown in FIG. 9, a gas suction port 2 provided at the top portion of a pump case 1 is in communication with an exhaust port 21 of a vacuum chamber 200. In this communication structure, a flange portion 1a provided around the top periphery of the pump case 1 is attached and fixed to the vacuum chamber 200 with a pump-chamber fastening bolt 30.
More particularly, several pump fastening bolt-holes 22 are equally spaced and formed around the chamber exhaust port 21 of the vacuum chamber 200, while the flange portion 1a of the vacuum pump 100 is formed so as to surround the gas suction port 2 and bolt-holes 3 are equally spaced and formed at the flange portion 1 so as to correspond to several pump fastening bolt-holes 22. The pump-chamber fastening bolt 30 is inserted and screwed from the lower side of the flange portion 1a into the pump fastening bolt-holes 22 through each bolt-holes 3, thereby attaching and fixing the vacuum chamber 200 to the vacuum pump 100. The gap between the shank of each fastening bolt 30 and the inner wall of the corresponding fastening bolt-hole 3 is set in accordance with the normal standardized sizes of a bolt and a bolt-hole. For example, the bolt-hole 3 is formed to have a diameter of 11 mm for the shank of the bolt 30 having a diameter of 10 mm.
A base member 4, which is separated from the pump case 1, is provided at the lower side of the pump case 1. Similarly to the connecting structure between the vacuum pump 100 and the vacuum chamber 200, the connecting between the separated base member 4 and the pump case 1 are performed by that a flange shaped base fastening portion 1b formed at the bottom periphery of the pump case 1 is fastened and fixed to the separated base member 4 by bolts (not shown).
In the vacuum pump 100 attached and fixed to the vacuum chamber 200, the rotor shaft 5 rotates at high speed together with the rotor 6 and the rotor blades 7 when the vacuum pump 100 is in operation. With this structure, the interaction between the rotor blades 7 rotating at high speed and the stator blades 8 and the other interaction between the rotor 6 rotating at high speed and the screw stator 10 having the screw grooves 10a cause gas molecules in the vacuum chamber 200 to pass through the gas suction port 2 and subsequently the pump case 1, and to be eventually exhausted from the pump exhaust port 11.
A light alloy is generally used and, in particular, an aluminum alloy is widely used as the structural material of the rotor 6, the rotor blades 7, the stator blades 5 and so forth which form the vacuum pump 100, since the aluminum alloy is excellent in machining and can be precisely processed without difficulty. However, the hardness of aluminum alloy is relatively low as compared with other materials used for the structural material, and accordingly aluminum alloy may cause a creep fracture depending on the operating condition. Also, a brittle fracture may occur mainly caused by a stress concentration at the lower portion of the rotor 2, when the vacuum pump is in operation.
In the conventional vacuum pump 100 having the above-described structure, when a brittle fracture occurs in the rotor 6 rotating at high-speed, for example, and a part of the rotor 6 crashes into the screw stator 10, since the screw stator 10 has an insufficient strength against a shock load caused by this crash, the screw stator 10 cannot absorb such a shock load and therefore radially moves and crashes into a base member 4. Accordingly, this shock load produces a high rotating torque (hereinafter, referred to as xe2x80x9cdamaging torquexe2x80x9d) which causes the entire vacuum pump to rotate and which causes problems in that the entire pump case 1 is distorted, the fastening bolts 30 fastening the vacuum pump 100 to the vacuum chamber 200 are broken by this distortion torque, and the vacuum chamber 200 is broken by the large damaging torque transferred thereto.
The present invention is made to solve the above-described problems. Accordingly, it is an object of the present invention to provide a vacuum pump which reduces a damaging torque produced and prevent transferring of the damage torque to the outside when a rotor rotating at high-speed crashes into a screw stator or the like so as to prevents a vacuum chamber or the like from being broken by the damaging torque transferred to the vacuum chamber or the like.
A vacuum pump according to the present invention comprises: a rotor 6; a pump case 1 surrounding the rotor; a flange portion 1a formed around the top periphery of the pump case; a plurality of pump fastening holes 22 provided at a periphery of an exhaust port 21 of a vacuum chamber 200 facing the upper surface of the flange portion; a plurality of vacuum chamber fastening bolt-holes 3 provided in the flange portion 1a so as to correspond to the pump fastening holes 22, said vacuum chamber fastening bolt-holes being passed through with a pump-chamber fastening bolt 30; a base fastening portion 1b formed around the bottom periphery of the pump case; a base 4 covering the lower side of rotor 6 and facing the lower surface of the base fastening portion 1b; a plurality of pump case-base member fastening holes 17 and 18 provided so as to correspond to the base fastening portion 1b and the base 4, respectively; and a plurality of pump case-base member fastening bolts 19 for fastening the pump case 1 and the base 4 by inserting and screwing into the pump case-base member fastening holes 17 and 18; wherein the dimensional relationships between the diameter of each bolt-hole and that of the shank of the corresponding bolt satisfy both or either one of the following conditions (a) and (b):
(a) a vacuum chamber fastening bolt-hole 3 has a larger diameter than the shank diameter 30d of the corresponding pump-chamber fastening bolt 30 by 20% or more; and
(b) a bolt-hole, which is either one of the pump case-base member fastening bolt-holes 17 and 18 provided in the base fastening portion 1b and the base 4, has a larger diameter than the shank diameter 19d of the corresponding pump case-base member fastening bolt 19 by 20% or more.
A vacuum pump according to the present invention further comprises: a rotor 6; a pump case 1 surrounding the rotor; a flange portion 1a formed around the top periphery of the pump case; a plurality of pump fastening holes 22 provided at a periphery of an exhaust port 21 of a vacuum chamber 200 facing the upper surface of the flange portion; a plurality of vacuum chamber fastening bolt-holes 3 provided in the flange portion so as to correspond to the pump fastening holes 22, said vacuum chamber fastening bolt-holes being passed through with a pump-chamber fastening bolt 30; a base fastening portion 1b formed around the bottom periphery of the pump case; and a plurality of pump case-base member fastening bolts 19 for fastening the pump case 1 and the base 4 by inserting and screwing into the pump case-base member fastening holes 17 and 18, wherein the positional relationships between the fastening bolt-holes and the corresponding fastening bolt satisfy both or either one of the following conditions (a) and (b):
(a) when the pump case 1 turns moved by a damaging torque, the gaps between the pump-chamber fastening bolts 30 and the corresponding vacuum chamber fastening bolt-holes 3 with respect to the turning direction of the pump case moved by the damaging torque are distributed within the range of 10% of the shank diameter of the bolt; and
(b) when the pump case turns moved by a damaging torque, the gaps between the pump case-base member fastening bolts 19 and the corresponding bolt-holes 17 and 18 with respect to the turning direction of the pump case moved by the damaging torque are distributed to the ranges including the range of 10% of the shank diameter of the bolt.
In the vacuum pump according to the present invention, the gap between each fastening bolt and the corresponding bolt-hole satisfies both or either one of the following conditions (a) and (b):
(a) a buffer member 50 is inserted into the gap between each pump-chamber fastening bolt 30 and the corresponding vacuum pump fastening bolt-hole 3; and
(b) a buffer member 50 is inserted into the gap between each pump case-base member fastening bolt 19 and the corresponding fastening bolt-hole 17 and 18.
With this configuration, the buffer members 50 absorb the damaging torque.
According to the present invention, the fastening bolts may satisfy both or either one of the following conditions (a) and (b):
(a) the pump-chamber fastening bolts are reduced diameter shank bolts; and
(b) the pump case-base member fastening bolts are reduced diameter shank bolts.
With this arrangement, the extending property of the reduced diameter shank bolts contributes to reducing the damaging torque.
According to the present invention, the fastening bolts satisfy both or either one of the following conditions (a) and (b):
(a) the pump-chamber fastening bolt 30 is an reduced diameter shank bolt; and
(b) the pump case-base member fastening bolt 19 is an reduced diameter shank bolt.
With this configuration, the characteristic of the reduced diameter shank bolt contributes to absorbing of damaging torque.
A joint structure of a vacuum pump according to the present invention comprises: a plurality of pump fastening holes 22 provided at periphery of an exhaust port 21 of a vacuum chamber 200; a flange portion 1a formed around the top periphery of the pump case 1, which surrounds the rotor 6 of the vacuum pump; a plurality of vacuum chamber fastening bolt-holes 3 provided in the flange portion 1a so as to correspond to the pump fastening holes 22; and a plurality of pump-chamber fastening bolts 30 for fastening the periphery of the exhaust port 21 of a vacuum chamber and the flange portion 1a by inserting and screwing into the pump fastening holes 22 and the pump fastening holes 22, wherein either diameter of the pump fastening holes 22 and the vacuum chamber fastening holes 3 has a larger diameter than the shank diameter 30d of the corresponding pump-chamber fastening bolt 30 by 20% or more.
A joint structure of a vacuum pump according to the present invention comprises: a plurality of pump fastening holes 22 provided at periphery of an exhaust port 21 of a vacuum chamber 200; a flange portion 1a formed around the top periphery of the pump case 1, which surrounds the rotor 6 of the vacuum pump; a plurality of vacuum chamber fastening bolt-holes 3 provided in the flange portion 1a so as to correspond to the pump fastening holes 22; and a plurality of pump-chamber fastening bolts 30 for fastening the periphery of the exhaust port 21 of a vacuum chamber and the flange portion 1a by inserting and screwing into the pump fastening holes 22 and the pump fastening holes 22, wherein when the pump case 1 turns moved by a damaging torque, the gaps between the pump-chamber fastening bolts 30 and the corresponding vacuum chamber fastening bolt-holes 3 with respect to the turning direction of the pump case moved by the damaging torque are distributed to the ranges including the range of 10% of the shank diameter of the bolt.
In the joint structure of a vacuum pump according to the present invention, a buffer member 50 is inserted into the gap between each pump-chamber fastening bolt 30 and the corresponding bolt-hole which is either one of the vacuum chamber fastening hole 3 and the pump fastening hole 22. With this arrangement, the buffer members 50 contribute to absorbing of damaging torque.
In the joint structure of a vacuum pump according to the present invention, the pump-chamber fastening bolt 30 is a reduced diameter shank bolt. With this arrangement, the extending property of the reduced diameter shank bolts the reduced diameter shank bolt contributes to absorbing of damaging torque reducing the damaging torque.
In this description, a hole such as a flange portion fastening hole, a pump fastening hole or a pump case-base member fastening hole means a screw hole which engages with the male-threaded portion of corresponding bolt or a bolt-hole which allows the shank of the corresponding bolt to pass therethrough and which has a larger diameter than the shank diameter. Also, fastening holes are used in the following two combinations:
(1) A Combination of a Bolt-hole and a Screw Hole:
The male-threaded portion of a bolt passing through the bolt-hole is screwed into and fastened to the female-treaded portion of the screw hole.
(2) A Combination of a Pair of Bolt-holes and a Nut:
The male-threaded portion of a bolt passing through the pair of bolt-holes is screwed into and fastened to the nut.
Also, in this present invention, when a bolt has a shank between the bolt head and the male-threaded portion thereof, a shank diameter of the bolt is defined by the diameter of the shank having no thread thereon, and when the bolt has no shank between the bolt head and the male-threaded portion thereof, a shank diameter is defined by the diameter of the crest of the male-threaded portion. A shank diameter of a reduced diameter shank bolt is defined by the diameter of its reduced-diameter portion. It will be apparent to those skilled in the art that bolts include not only strictly defined ones but also rod-like screws such as a machine screw.
According to the present invention, when the damaging torque causes the entire vacuum pump to turn, the inner surfaces of the bolt-holes closest to the outer surfaces of the corresponding pump-chamber fastening bolts first come into contact with these outer surfaces, and start causing these bolts to be deformed and broken. Subsequently, the other portion of the inner surfaces of the bolt-holes second closest the outer surfaces of the corresponding pump-chamber fastening bolts come into contact with these outer surfaces, and start causing these bolts to be deformed and broken. Similar deformations and breaking of the bolts sequentially occur contacted by the bolt-holes whose outer surfaces are sequentially spaced away from the corresponding bolts. During this deformation and breaking process of the bolts, the damaging torque is absorbed and also the peak value of the breaking toque is reduced.